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My block is a 12555506 and the Date code is M039
These numbers came off the driver and passenger back of engine behind the heads.


Who made the blocks with the M039 or does anyone know what it is?
 

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The "MO39 ",decypherd will supply the day,month & year of the casting. The VIN will also be on the block top so more can info can be determined by the VIN.IIRC the 506 was produced several years.1999/2000 years should be good ones. For my own use I would seek a #141 cast in 1996.Has the "small " outside main bolts.less prone for cracking the block.1999/2000 years should begood as they recieved the final cooling system upgrades by GM. AFAIK GM cast all blocks till they had Navastar do them at the last of 2000.I have a 506 block/engine produced in 2000.It is complete ,61k mi. & I would like to sell it.
 

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If it is possible, check in the valley of your block, to see if the Navistar emblem is cast in to it. Also, should have 506 cast (with dots) on the side of the valley...... if you could post up some pics with the intake removed, it would aid us, as our info is a little sketchy. Without the pics, the best we can do is; 2005 March 9.
 

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My block is a 12555506 and the Date code is M039
These numbers came off the driver and passenger back of engine behind the heads.


Who made the blocks with the M039 or does anyone know what it is?
Made by GM, casting dates are represented by a letter (month, "A" = January, "B"= February, "I" is not used) two digits (day of month) and a single digit (last digit of year)

Your block was cast on December 03, 1999.
 

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So my block is at risk of having the number 8 cylinder problems?

Why dont they use I?
"I" could be mistaken for "1", so is not used. "M" = 12th month.

I have no idea as to the risk of #8 cylinder problem, but appears as though your engine has gone 11 years now without any major problem, may go another 11, who knows?
 

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Yes Bob is entirely correct as to the year of your block.

The reason I was asking for the valley markings, was that after Navistar began casting the blocks , they discontinued the use of the Julien calender date markings. This was for the blocks after 2000, with; ## indicating the month, ## indicating the day and the year indications were letters, starting with H for 2001, no I or O......

It did not matter however, if I was paying enough attention I would have realized the # to letter sequence was pre-Navistar....:)

So the moral is #'s before letters on date code, Navistar casting.:D
 

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So my block is at risk of having the number 8 cylinder problems?

Why dont they use I?
#8 cylinder is not the problem with that block, its the bottom end cracking through the piston squirters into the water jacket that it is highly prone to and the 99-2001 gm blocks changed the main caps and were prone to breaking the #2 main cap in half.

#8 cyl problem was mostly the blocks before 506 with the smaller cooling system
 

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#8 cyl problem was mostly the blocks before 506 with the smaller cooling system
Which blocks came before 506, the 141?
 

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'Engine Builder' magazine did an article on the GEP Optimizer back in June 2007: http://www.enginebuildermag.com/Article/1458/the_optimizer_6500.aspx (article is supported with photos)

In the article they discussed some of the main problems with the GM 6.5 blocks. Although the article doesn't reference particular block #'s, in some cases you can infer which blocks are being discussed based on the design description given, e.g; Piston Cooling Jets:

"While machining for piston oiler holes in the main bearing saddles, tooling would occasionaly contact the bottom of the cylinder bores, causing stress risers that have led to cracking"

If I'm not mistaken, the only 6.5 diesel blocks produced by GM with the oiler jets was the 506. - Apparently though, not all 506 blocks were affected, as it was an "occasional" problem - Luck of the draw there I guess.
 

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'Engine Builder' magazine did an article on the GEP Optimizer back in June 2007: http://www.enginebuildermag.com/Article/1458/the_optimizer_6500.aspx (article is supported with photos)

In the article they discussed some of the main problems with the GM 6.5 blocks. Although the article doesn't reference particular block #'s, in some cases you can infer which blocks are being discussed based on the design description given, e.g; Piston Cooling Jets:

"While machining for piston oiler holes in the main bearing saddles, tooling would occasionaly contact the bottom of the cylinder bores, causing stress risers that have led to cracking"

If I'm not mistaken, the only 6.5 diesel blocks produced by GM with the oiler jets was the 506. - Apparently though, not all 506 blocks were affected, as it was an "occasional" problem - Luck of the draw there I guess.
the tooling did not cause it, it was gm taking them right from the foundry and machining them without letting them cure first to keep up with the demand, as they cured after being machined it then had the stress risers.
 

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That's interesting, I didn't know that freshly cast engine blocks needed time to cure. Why exactly do they need to cure? How much time do they typically need?

The article is fairly persuasive as it has a photo of (allegedly) a 506 block showing a tooling 'nick' at the bottom of the cylinder bore.

I'm curious to know how you learned about this? There's so much misinformation out there it can be vexing to sort the facts from the myths, especially when two totally differing accounts seem equally plausible.
 

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#141 block casting was in late 1996 truck production. My march 96 assembled 96 has one in it. It has been an absolutly stable block/heads. ,now over 180.00 miles.& has factory dual thermostats.To my knowledge NO Navastar blocks were installed in the regular production trucks. They were supplied in some warranty paid replacements around Y2K.
 

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If you would like to know more about cast iron, aging , creeping, shifting, curing,settling, internal stress, ect. Ask an old time machinist or look up Rolls Royce site and read about heating and cooling cycles,before machining and after. Green iron moves, Its a fact of life.
I have dealt with it for most of my life, machinist , engine builder.
 

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That's interesting, I didn't know that freshly cast engine blocks needed time to cure. Why exactly do they need to cure? How much time do they typically need?

The article is fairly persuasive as it has a photo of (allegedly) a 506 block showing a tooling 'nick' at the bottom of the cylinder bore.

I'm curious to know how you learned about this? There's so much misinformation out there it can be vexing to sort the facts from the myths, especially when two totally differing accounts seem equally plausible.
the info came directly from bill heath, from what i remember from the conversation when i called about my 506 block and girdles (he says stay far away from them btw)they need to cure because as the casting cools and hardens the metal still shifts, if not allowed to cure fully and is machined it then distorts as it finishes curing
 

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If it is possible, check in the valley of your block, to see if the Navistar emblem is cast in to it. Also, should have 506 cast (with dots) on the side of the valley...... if you could post up some pics with the intake removed, it would aid us, as our info is a little sketchy. Without the pics, the best we can do is; 2005 March 9.

Okay, reviving a dead thread, I have a 6.5 casting #12555506, date code L046, vin 1GCGC33F0VF016324 came out of a 1997 C3500, going to be installed in a 1986 M1028A3 dually. How do you read the dots in the lifter galley?

Is this a 141?
 

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#141 block casting was in late 1996 truck production. My march 96 assembled 96 has one in it. It has been an absolutly stable block/heads. ,now over 180.00 miles.& has factory dual thermostats.To my knowledge NO Navastar blocks were installed in the regular production trucks. They were supplied in some warranty paid replacements around Y2K.
Hoping mine is a #141
 

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Okay, reviving a dead thread, I have a 6.5 casting #12555506 - - - Is this a 141?
Its a 506..
 
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